This invention relates to a drive unit for driving the developing device of a color image forming apparatus by electrophotography and for pressing or releasing the cleaning means and the transfer belt.
Various methods and apparatuses for producing color images by electrophotography have been proposed. Japanese Patent Publications Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publications) No. 100770/1986, for example, indicates a method that latent images are formed and developed on the photosensitive drum which is an image carrying member according to the number of decomposed colors of the original image, each latent image is transferred to a transfer drum each time it is developed to form a multi-color image on the transfer drum, and the multi-color image is transferred to a recording paper to obtain a color copy. An apparatus using this method is required to mount a transfer drum large enough to transfer an image on the peripheral surface in addition to the photosensitive drum, and hence the apparatus inevitably becomes large and structurally complicated.
Japanese Patent O.P.I. Publications No. 149972/1986, for example, indicates a method that latent images are formed and developed on the photosensitive drum according to the number of decomposed colors of the original image, and a color toner image is transferred to the transfer material, each time it is developed, to obtain a multi-color copy. This method is difficult in keeping accurate registration of multi-color images and cannot produce a quality color copy.
There is another method available that the processing that latent images are formed on the photosensitive drum according to the number of decomposed colors of the original image and developed by color toners is repeated to registrate color toner images on the photosensitive drum, and the registrated color toner images are transferred to obtain a color image. The basic process of this multi-color image forming method is indicated in Japanese Patent O.P.I. Publications Nos. 75850/1985, 76766/1985, 95456/1985, 95458/1985, and 158475/1985 by the grantee of the present invention.
A multi-color image forming apparatus for obtaining color images by this registration method is equipped with a plurality of developing devices containing different color toners on the periphery of the photosensitive drum. The photosensitive drum generally rotates more than once and latent images on the photosensitive drum are developed to produce color images.
A plurality of developing devices containing different color developers respectively which are mounted on the periphery of the photosensitive drum operate alternately for forming images and develop latent images to form toner images. During development, the development bias voltage is applied to the development sleeve by rotating the development sleeve and the stirring roller. Each of a plurality of developing devices is equipped with a drive motor for rotating it, and the ON or OFF operation of the motor is automatically controlled. Or, one motor is used as a power source to transfer power to a plurality of developing devices, ON-OFF switching means using an electromagnetic clutch or ON-OFF switching means using a solenoid and a spring clutch are mounted between the power transfer systems, and the rotation of the developing devices is controlled by operating the switching means.
Since toners are consumed by development during image forming, if the development is continuously performed without supplying toners, the toner ratio of the developer decreases when a two-component developer is used and quality images cannot be obtained. Therefore, each developing device is connected to a toner box containing a toner. When the toner ratio of the developer in a developing device, for example, decreases, the toner is supplied from the toner supply box to the developing device.
To switch or drive the toner supply boxes, a small motor which is mounted on each toner supply box is used. The motor is driven for a predetermined time to supply the toner when a decrease of the toner density is detected. It causes an increase in cost to mount and operate motors for driving the developing devices and for driving or switching the toner supply boxes or to mount and electrically control expensive electromagnetic clutches. When a color image forming apparatus for registrating toner images on the photosensitive drum and transferring them on a recording paper is to be used, a transfer belt which is used as a transfer means and a blade and fur brush which are used as cleaning means are required to be kept away from the photosensitive drum while forming a toner image to prevent the toner image from damage. It is also required for forming the next image that the transfer belt is pressed to the photosensitive belt when the image forming is finished to transfer a toner image to a recording paper, and the cleaning means are pressed to the surface of the photosensitive drum for cleaning when the transfer is finished.
A pressing and pressing-release facility using a powerful solenoid or motor rotation is used for pressing or releasing the cleaning means and the transfer belt. When a powerful solenoid is used, electrical interferences such as noise occur. When a motor is used, the cleaning means and the transfer belt require complicated mechanisms and control and resultant high costs.